Bcl-2 prevents apoptotic mitochondrial dysfunction by regulating proton flux.
We and others have recently shown that loss of the mitochondrial membrane potential (Deltapsi) precedes apoptosis and chemical-hypoxia-induced necrosis and is prevented by Bcl-2. In this report, we examine the biochemical mechanism used by Bcl-2 to prevent Deltapsi loss, as determined with mitochondria isolated from a cell line overexpressing human Bcl-2 or from livers of Bcl-2 transgenic mice. Although Bcl-2 had no effect on the respiration rate of isolated mitochondria, it prevented both Deltapsi loss and the permeability transition (PT) induced by various reagents, including Ca2+, H2O2, and tert-butyl hydroperoxide. Even under conditions that did not allow PT, Bcl-2 maintained Deltapsi, suggesting that the functional target of Bcl-2 is regulation of Deltapsi but not PT. Bcl-2 also maintained Deltapsi in the presence of the protonophore SF6847, which induces proton influx, suggesting that Bcl-2 regulates ion transport to maintain Deltapsi. Although treatment with SF6847 in the absence of Ca2+ caused massive H+ influx in control mitochondria, the presence of Bcl-2 induced H+ efflux after transient H+ influx. In this case, Bcl-2 did not enhance K+ efflux. Furthermore, Bcl-2 enhanced H+ efflux but not K+ flux after treatment of mitochondria with Ca2+ or tert-butyl hydroperoxide. These results suggest that Bcl-2 maintains Deltapsi by enhancing H+ efflux in the presence of Deltapsi-loss-inducing stimuli.
Shimizu
S
S
Department of Medical Genetics, Biomedical Research Center, Osaka University Medical School, 2-2 Yamadaoka, Suita, Osaka 565, Japan.
Eguchi
Y
Y
Kamiike
W
W
Funahashi
Y
Y
Mignon
A
A
Lacronique
V
V
Matsuda
H
H
Tsujimoto
Y
Y
D000818:Animals; D017209:Apoptosis; D001693:Biological Transport, Active; D002118:Calcium / Q000494:pharmacology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007425:Intracellular Membranes / Q000502:physiology; D008564:Membrane Potentials; D051379:Mice; D008930:Mitochondria, Liver / Q000502:physiology*; D010085:Oxidative Phosphorylation; D010101:Oxygen Consumption; D010545:Peroxides / Q000494:pharmacology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000502:physiology*; D051381:Rats; D020122:tert-Butylhydroperoxide
D010545:Peroxides; D019253:Proto-Oncogene Proteins c-bcl-2; D020122:tert-Butylhydroperoxide; D002118:Calcium